Lens
The transparent structure inside the eye that focuses light rays onto the retina (the nerve layer that lines the back of the eye, senses light and creates impulses that go through the optic nerve to the brain). The lens was named after the lentil bean because it resembled it in shape and size. Aside from the lens, the eye has a number of other components. These include the cornea, iris, pupil, retina, macula, optic nerve and vitreous. The cornea is the clear front window of the eye that transmits and focuses light into the eye. The iris is the colored part of the eye that helps regulate the amount of light that enters the eye. The pupil is the dark aperture in the iris that determines how much light is let into the eye. The retina is the nerve layer that lines the back of the eye, senses light and creates impulses that travel through the optic nerve to the brain. The macula is a small area in the retina that contains special light-sensitive cells and allows us to see fine details clearly. The optic nerve is the nerve that connects the eye to the brain and carries the impulses formed by the retina to the visual cortex of the brain. The vitreous humor is a clear, jelly-like substance that fills the middle of the eye.
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1. A transparent material with one or both surfaces having a concave or convex curve; acts upon electromagnetic energy to cause convergence or divergence of light rays. 2. [TA] The transparent biconvex cellular refractive structure lying between the iris and the vitreous humor, consisting of a soft outer part (cortex) with a denser part (nucleus), and surrounded by a basement membrane (capsule); the anterior surface has a cuboidal epithelium, and at the equator the cells elongate to become l. fibers. SYN: crystalline l.. [L. a lentil]
- achromatic l. a compound l. made of two or more lenses having different indices of refraction, so correlated as to minimize chromatic aberration.
- acoustic l. in ultrasonography, a l. used to focus or diverge a sound beam; may be simulated by electronic manipulation of signals.
- aplanatic l. a l. designed to correct spherical aberration and coma (q.v.). SYN: periscopic meniscus.
- apochromatic l. a compound l. designed to correct both spherical and chromatic aberrations.
- aspheric l. a l. with a paraboloidal surface that eliminates spherical aberration.
- astigmatic l. SYN: cylindrical l..
- bandage contact l. a contact l. placed on the cornea to cover a defect.
- biconcave l. a l. that is concave on two opposing surfaces. SYN: concavoconcave l., double concave l..
- biconvex l. a l. with both surfaces convex. SYN: convexoconvex l., double convex l..
- bifocal l. a l. used in cases of presbyopia, in which one portion is suited for distant vision, the other for reading and close work in general; the reading addition may be cemented to the l., fused to the front surface, or ground in one-piece form; other bifocal lenses are the flat-top Franklin type, or blended invisible.
- cataract l. any l. prescribed for aphakia.
- l. clock SYN: Geneva l. measure.
- compound l. an optical system of two or more lenses.
- concave l. a diverging minus power l.. SYN: minus l..
- concavoconvex l. a converging meniscus l. that is concave on one surface and convex on the opposite surface.
- contact l. a l. that fits over the cornea and sclera or cornea only; used to correct refractive errors.
- convex l. a converging l.. SYN: plus l..
- convexoconcave l. a minus power l. having one surface convex and the opposite surface concave, with the latter having the greater curvature.
- convexoconvex l. SYN: biconvex l..
- corneal l. contact l. of plastic without scleral portions.
- crystalline l. SYN: l. (2).
- cylindrical l. (cyl., C) a l. in which one of the surfaces is curved in one meridian and less curved in the opposite meridian; e.g., a teaspoon or a football. SYN: astigmatic l..
- decentered l. a l. so mounted that the visual axis does not pass through the axis of the l..
- dislocation of l. SYN: ectopia lentis.
- double concave l. SYN: biconcave l..
- double convex l. SYN: biconvex l..
- eye l. the upper of the two planoconvex lenses of Huygens ocular. SYN: ocular l..
- field l. the lower of the two planoconvex lenses of Huygens ocular.
- foldable intraocular l. a l. often made of silicone or an acrylic polymer that may be doubled over for implantation into the eye following cataract removal.
- Fresnel l. a l. with a surface consisting of a concentric series of zones that duplicate the power of a l. or prism but with less thickness. SYN: lighthouse l..
- Hruby l. a non–contact l. mounted on a slitlamp used for evaluating the retina.
- immersion l. an objective (for a microscope) constructed in such a manner that the lower l. may be moved downward into direct contact with a fluid which is placed on the object being examined; by using a fluid with a refractive index closely similar to that of glass, the loss of light is minimized.
- lighthouse l. SYN: Fresnel l..
- meniscus l. a l. having a spherical concave curve on one side and a spherical convex curve on the other. SYN: articular crescent, articular meniscus, intraarticular cartilage (2), meniscus articularis, meniscus (1).
- minus l. SYN: concave l..
- multifocal l. a l. with segments providing two or more powers; commonly, a trifocal l..
- ocular l. SYN: eye l..
- omnifocal l. a l. for near and distant vision in which the reading portion is a continuously variable curve.
- orthoscopic l. a spectacle l. corrected for distortion and curvature of the periphery.
- periscopic l. a l. with 1.25 D base curve.
- photochromic l. a light-sensitive spectacle l. that reduces light transmission in sunlight and increases transmission in reduced light.
- planoconcave l. a l. that is flat on one side and concave on the other.
- planoconvex l. a l. that is flat on one side and convex on the other.
- plus l. SYN: convex l..
- safety l. a l. that meets government specifications of impact resistance; the increased impact resistance required for safety lenses is obtained by tempering, by an ion-exchange process, or by using laminated or plastic lenses.
- slab-off l. a spectacle l. with a base-up prism below; used in unequal myopia to equalize image displacement when reading.
- spherical l. (S, sph.) a l. in which all refracting surfaces are spherical.
- spherocylindrical l. a combined spherical and cylindrical l., one surface being spherical, the other cylindrical. SYN: spherocylinder.
- toric l. a l. in which both meridians are curved but not to the same degree.
- trial lenses a series of cylindrical and spherical lenses used in testing vision.
- trifocal l. a l. with segments of three focal powers: distant, intermediate, and near.

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lens also lense 'lenz n
1) a curved piece of glass or plastic used singly or combined in eyeglasses or an optical instrument (as a microscope) for forming an image by focusing rays of light
2) a device for directing or focusing radiation other than light (as sound waves, radio microwaves, or electrons)
3) a highly transparent biconvex lens-shaped or nearly spherical body in the eye that focuses light rays entering the eye typically onto the retina, lies immediately behind the pupil, is made up of slender curved rod-shaped ectodermal cells in concentric lamellae surrounded by a tenuous mesoblastic capsule, and alters its focal length by becoming more or less spherical in response to the action of the ciliary muscle on a peripheral suspensory ligament
lensed adj
lens·less adj

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n.
1. (in anatomy) the transparent crystalline structure situated behind the pupil of the eye and enclosed in a thin transparent capsule. It helps to refract incoming light and focus it onto the retina. See also accommodation.
2. (in optics) a piece of glass shaped to refract rays of light in a particular direction. Convex lenses converge the light, and concave lenses diverge it; they are worn to correct faulty eyesight. See also bifocal lens, contact lenses, trifocal lenses.

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(lenz) [L. “lentil”] a piece of glass or other transparent substance so shaped as to converge or scatter the rays of light, especially the glass used in appropriate frames or other instruments to increase the visual acuity of the human eye. See also glasses and spectacles. [TA] the transparent biconvex body of the eye situated between the posterior chamber and the vitreous body, constituting part of the refracting mechanism of the eye. Called also l. crystallina or crystalline l.

Lenses: (A–F), Spherical lenses: (A), biconvex; (B), biconcave; (C), planoconvex; (D), planoconcave; (E), concavoconvex, periscopic convex, converging meniscus; (F), convexoconcave, periscopic concave, diverging meniscus; (G, H), cylindrical lenses, concave and convex.

Lens of eye.


Medical dictionary. 2011.

Look at other dictionaries:

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  • LENS — Graece φακῆ, tenuiorum et Philosophorum cibus, Cynicorum praesertim, olim fuit, cuius encomium vide apud Athen. l. 4. c. 18. Sed et edulio eius tantopere in sacris Esavus legitur gavisus, ut iure primogentiurae illud redimere profanus homo non… …   Hofmann J. Lexicon universale

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  • lens — ► NOUN 1) a piece of transparent material with one or both sides curved for concentrating or dispersing light rays. 2) the light gathering device of a camera, containing a group of compound lenses. 3) Anatomy the transparent elastic structure… …   English terms dictionary

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